Vehicle climate control systems typically include a microprocessor-based controller programmed to adjust the cooling capacity of the system based on a measure of the cabin air temperature and various other factors such as outside air temperature and solar loading. Solar loading is ordinarily measured by mounting one or more photovoltaic sensors under the windshield of the passenger compartment for producing a signal representative of the solar load on the passenger compartment. In current practice, the photovoltaic sensor comprises sensing element packaged in a spherical housing made of translucent plastic that passes attenuated visible light. The sensing element produces an electrical voltage that varies with the intensity of the impinging light, and the controller uses the voltage as a measure of solar loading.
Although a photovoltaic sensor of the type described above can provide a reliable measure of incident visible light, it does not necessarily provide a true indication of solar loading because it fails to take into account infrared radiation due to hot ambient and passenger compartment surfaces. Additionally, photovoltaic sensors are relatively expensive compared to mass-produced devices such as thermocouples or thermistors. Accordingly, what is needed is a more accurate and cost-effective way of detecting passenger compartment heating due to solar radiation and compensating the cooling capacity of a climate control system accordingly.